Heretofore, acoustic and other transducers, including loudspeakers, compression drivers, light sources and sources of electromagnetic radiation such as antennas or klystron devices, have made use of a myriad of methods to convert electric signals from one form to another or, in the case of acoustic transducers to convert electric signals to acoustic signals. For example, the vast majority of acoustic transducers operate by electromagnetically coupling an electric signal to a diaphragm in order to create the acoustic signal. A primary deficiency of these acoustic transducers is their frequency dependent beamwidth. In the case of electromagnetic transducers, a uniform controlled beamwidth and the elimination of interference between multiple transducers is crucial to improved signal reception and reproduction. In general, the beamwidth of many state-of-the-art acoustic and electromagnetic transducers is a function of the frequency of vibration and the size of the vibrating element.
Because of the interdependence of transducer size, frequency, and beamwidth, typical acoustic transducer systems (such as a loudspeaker) utilize a multiple transducer arrangement to produce an acceptable beamwidth throughout the frequency range of human hearing. A primary deficiency in this use of multiple transducers is that the physical size of a transducing element places a constraint on how closely together in spatial alignment multiple transducers can be located with respect to one another. This constraint results in interference between the radiated energy fields of different transducers at frequencies where the transducers overlap, which in the case of an acoustic transducing system causes a degradation in the overall sound quality that is detectable by the human ear. This interference is due to the unequal pathlengths traveled by radiated energy waves that emanate from two different sources but which come together at the same point. Therefore in the case of acoustic transducers, it is crucial to sound quality to locate multiple transducers in as close a spatial alignment as possible. This will minimize the interference between transducers and create an overall sound pattern that mimics the actual sound source as closely as possible.
Recently a transducing system has become available (U.S. Pat. No. 4,421,200) which controls beamwidth dependence by using a reflective component shaped as a section of elliptical cross sections that have radially oriented distinct focal points and share a common focal point. Transducers placed at the distinct focal points have their acoustic or electromagnetic radiation redirected to the common focal point. By selecting the parameters of the ellipses and their orientation with respect to one another, the redirected energy, appearing to emanate from the common focal point, can be made to have a nearly constant beamwidth, irrespective of the frequency dependent beamwidth of the transducers placed at the distinct focal points. The beamwidth of the redirected energy in this novel transducing system is fixed by the parameters of the ellipses shaping the reflective component, and thus is not variable. Moreover, it may not be possible to reflect all the radiation emitted from the transducers, resulting in interference between the reflected and non-reflected radiation.
Another new transducing system (U.S. Pat. No. 4,629,030) utilizes a reflective component with a surface defined by an ellipse that is rotated about an axis of revolution which lies in the plane of the ellipse, and which is oriented at any finite angle with respect to the major axis of the ellipse. This axis of revolution contains the focal points that are common to the ellipse as it is rotated. This reflective component is characterized by a common focal point as well as a focal curve. By placing a transducer at the common focal point, electromagnetic or acoustic radiation is redirected by the reflective component and focused on the focal curve, causing the focal curve to appear as the source of the radiation. Conversely, electromagnetic or acoustic radiation emitted from a transducer placed at the focal curve will be focused on the common focal point. In that case, the common focal point appears to be the source of the radiation. This transducing system also has a fixed beamwidth determined by the parameters of the ellipse shaping the reflective component. It is also possible for the redirected energy to be degraded by interference with electromagnetic or acoustic radiation which emanates from the transducer but does not strike the reflective component.
Yet another new transducing system (U.S. Pat. No. 4,836,328) utilizes a reflective component with a surface defined by a parabola that is rotated about an axis of revolution that lies in the plane of the parabola and is oriented parallel to the major axis of the parabola. The reflective component is characterized by a focal curve. Electromagnetic or acoustic radiation emanating from a transducer placed perpendicular to both axes will be redirected by the reflective component and focused on the focal curve, causing the focal curve to appear as the source of the radiation. Conversely, electromagnetic or acoustic radiation from a transducer placed at the focal curve will be redirected as if emanating from a plane wave. This transducing system is also has a fixed beamwidth determined by the parameters of the parabola shaping the reflective component, and it is possible that the redirected energy may be degraded by interference with electromagnetic or acoustic radiation which emanates from the transducer but does not strike the reflective component.
All of the above transducer systems, including those which produce a substantially invariant beamwidth throughout their frequency range, are limited when used in multiple transducer extended frequency bandwidth devices, since the physical size of the transducing elements does not allow them to be closely spatially aligned, causing interference at those frequencies where the transducers overlap.
The invention described herein provides for a method to improve the above described transducing systems for use in multiple transducer extended frequency bandwidth devices, by providing a means to focus and redirect the output of multiple transducers into a more localized area, thereby minimizing the interference normally created by the use of multiple transducers. The invention utilizes a novel reflective component, which has a surface defined by the coincident surfaces of revolution of an ellipse and a parabola, and which is characterized by two distinct focal curves (which may be coincident) and a single focal point, common to the elliptical surface. Multiple transducers placed in positions as described below will have their radiation appearing to emanate from these focal curves. The virtual sources of the radiation are the focal curves, which are substantially closer in spatial alignment than the transducers themselves, largely eliminating the interference that would be experienced if two separate, constant beamwidth transducers were used without the reflective shell. The overall output of this arrangement minimizes the interference between the multiple transducers at overlapping frequencies, while at the same time maintaining the substantially frequency invariant beamwidths known to be gained by the use of such reflective surfaces.
The invention described herein also provides for a method to improve these transducing systems by providing a means for varying and directing the beamwidth of the redirected acoustic or electromagnetic energy without altering the parameters of the reflective component, and by providing a means to attenuate or eliminate the energy which emanates from a transducer but does not strike the reflective component.
Accordingly, it is an object of this invention to provide a device which will minimize interference from multiple transducers, by utilizing a reflective component to focus acoustic or electromagnetic radiation emitted from the transducers into focal curves that are in closer spatial alignment with one another than the transducers themselves, while at the same time maintaining the substantially frequency invariant beamwidths found in the use of such reflective components.
It is another object of this invention to provide a reflective component which will minimize interference from multiple transducers, including a means of varying and directing the beamwidth of acoustic or electromagnetic radiation emitted from the transducing system without altering the parameters of the reflective component, and including an acoustic or electromagnetic absorbing element which will attenuate or eliminate that radiation emitted from a transducer which would not otherwise strike the reflective component.